The subject of the invention is a method in which the transport of heat occurs from a heat source with limited maximum temperature to a heat consumer (heat-admitting process) operating at even higher temperature by means of a mostly gaseous heat carrier (heat carrier fluid), preferably led in circulation.
Preliminarily, several concepts must be distinguished:
(1) Gas Turbine Concept
The concept "gas turbine" is generally used not only for a turbine in which a gaseous work fluid expands and delivers work, but also for a motor which consists of compressor, heater or combustion-chamber and turbine. Throughout this specification, the first definition will be used.
(2) Gas Turbine-Power Process
The process occurring in the second type of "gas turbine" is characterized in that the work fluid will be heated to a high temperature between the compressor and turbine by introduction of heat from externally (closed process) or through burning of fuel in a combustion-chamber ("internal combustion engine"). Since the temperature--and thereby the volume--of the work fluid is greater with the expansion than with the compression, the work furnished by the turbine is greater than the work received by the compressor: altogether the power machine "gas turbine" delivers work externally. This effective work is greater the higher the turbine--and the lower the compressor--entry temperature. In the case of the closed processes the work fluid must be re-cooled after the expansion before entry again into the compressor. In the case of the open processes the exhaust gas will be led away after the expansion into the environment, and the compressor will suck in fresh air: The "re-cooling" is accomplished in the atmosphere. The power machine process is thus composed of the steps: compression (in the compressor), introduction of heat (in the heater or furnace), expansion (in the turbine), leading away of heat (in the cooler or into the atmosphere).
(3) Cold Gas-Cold Process
With this process the gaseous work fluid flows through the compressor and turbine components in the same succession as with the power machine process. However, heat will not be introduced between these components, but rather removed, and thereby the temperature will be lowered before the expansion. After the expansion, thus at the exit of the turbine, the work fluid has a lower temperature than it had upon entry to the compressor. Heat must thus be introduced into it before the renewed entry into the condensor. Since this process will be used at temperatures below the temperature of the surroundings, one speaks of the heat transferred to the work fluid at the lowest process temperature as being "the produced cold" and the process as being a "cold process".
Since with this process the temperature is higher with the compression than with the expansion, the compressor work is greater than the turbine work; the process must therefore have work introduced from externally.
(4) Heat Pump
In a heat pump in principle the same process takes place, with the same order of succession of compressor, heat withdrawal, expansion, heat admission as in the cold gas-cold process. It is thus a work-receiving process. It is distinguished only with respect to three points:
The heat admission occurs at environmental temperature and by no means goes below this temperature. The useful heat delivered by the pump is accordingly at higher temperature (heating temperature). Lower and upper temperature levels are thus higher than with the cold gas-cold process. Moreover, heat pump processes in customary manner are managed with circulating fluid which vaporizes during heat admission and condenses during heat emission, thus effecting phase changes twice during each cycle. This is not the case with the other described processes.
For the most part a throttle will be used for the expansion, since the process involves temperature levels which do not allow for recovery of a portion of the work of compression through the work-producing expansion; in addition, complications result in turbine expansion of an almost boiling fluid.
(5) High Temperature Heat Pump
The high temperature heat pump process is so named since with the addition of work the temperature of the circulating fluid is raised in the compressor the same as in a heat pump process. However, the high temperature heat pump process operates in a much higher temperature range. Also, the temperature is still sufficiently high after the discharge of heat to the heat-admitting process for recovery of a portion of the work employed in the compression by means of the expansion. In addition, after the expansion the temperature is still sufficiently high to transmit heat into a thermal power process. The circulating fluid remains in the gaseous phase. The primary purpose of the high temperature heat pump is to bring this gas to a higher temperature without the introduction of heat from external sources.
In many cases the temperature on the one hand which can be delivered with the heat from a heat source is upwardly limited (e.g. with chemical or nuclear reaction or through the hot strength of the material for the heat exchanger); on the other hand, it is often the case for a heat consumer that the temperature with which the heat will be introduced is of greatest significance (e.g. with coal gasification processes or with endothermic chemical reactions). Such an upward temperature limitation has for the heat consumer the disadvantage that the rate of reaction of the heat-admitting reaction will be inhibited. Then, either the reactor for this reaction must be built larger, or a decrease in performance must be accepted. One therefore strives to raise the temperature of the heat-admitting reaction, which, however--as will subsequently be demonstrated--is not very easy. It is customary to transport heat from a heat-source to a heat-consumer using a gaseous heat carrier, since heat-source and heat-consumer must be separated from one another. The local separation can thus be essentially chemical, industrial processing or based upon other grounds. The heat carrier can be used once, or, introduced in circulation, repeatedly. The losses of heat occurring with the heat transfer from the heat source to the heat carrier and from the heat carrier to the heat consumer, as well as with the transport of heat itself, result in an introduction of heat into the heat consumer at a lower temperature than that of the heat source. The loss of pressure occurring with the transport of heat is balanced through the use of blowers.
A further problem existing with such high temperature processes, in which e.g. a chemical product is produced, such as gas from coal, is that the heat carrier, after delivery of heat in the high temperature process, still has relatively high temperature, which, on efficiency grounds, must be downwardly cooled. This may be done e.g. during generation of electrical energy. In such cases the yield of chemical products of the heat-admitting reaction and the yield of electrical energy from the entire process are thus coupled with each other. This coupling has disadvantages for the operation of the entire installation when chemical products and electrical energy are not consumed simultaneously in accordance with their production.
It is now known that with the compression of gases their temperature increases, and that work must be expended in order to compress them. It is further known that this work of compression can be performed by a gas turbine, which will be loaded with the same fluid as the compressor. It is conclusively known that in a heat pump process the temperature of the heat carrier gas will be lowered through removal of heat between the compressor and the gas turbine; thereby the gas temperature at the outlet of the gas turbine is lower than the compressor entry temperature. Since the work of the gas turbine alone is not sufficient to drive the compressor, work must be introduced to the compressor-turbine-set. (German Offenlegungsschrift DE-OS 27 55 092). With such heat pump processes the work to be performed in the compressor must, however, be furnished in a relatively uneconomical manner, namely from an energy source which works at a much higher temperature level than is obtained by the heat pump itself; moreover, the final temperature obtained, as is well known, corresponding to the previously considered significant entry zone, is relatively low.